The invention relates generally to leak detection equipment and more specifically to leak detection equipment for determining the existence of leaks in irregularly shaped containers for fluids and semi-fluid substances, for example, food, and the like and a method of leak detection.
Leak detection of containers is task specific in that the test must be specialized and adapted to not only the configuration of the container but also of the product disposed therewithin. Numerous factors fall under the first consideration, such as the shape of the container, the material from which the container is fabricated and the closure of the container, including not only how the closure is sealed upon fabrication and filling of the container but also how the closure is opened. With regard to the product itself typical factors are the density of the material, the air content either within the material or remaining within the container above the product, whether the material freezes or exhibits other temperature dependent behavior, whether the material is dry, moist or liquid, and solid, viscous or fluid. Clearly, the leak detection process must respond to these and other container/closure/product considerations.
In the prior art, many disclosures relate to leak detection schemes in which pressure is applied to a flexible container to determine whether the container integrity is such that internal pressure resists the force or the container fails and collapses because of a leak. For example, U.S. Pat. No. 4,148,213 to Prakken utilizes a conveyor belt to apply force to flexible packages, senses those packages which do not resist the applied force and moves them from between the conveyor belts by an air stream. U.S. Pat. No. 4,510,730 to Edmondson compresses a flexible package between opposed pressure members and senses the degree of closure of the pressure members. Members which close about a package more than a predetermined amount indicate the presence of a non-sealed container. U.S. Pat. No. 4,756,184 to Reishus et al., owned by the assignee herein, teaches an apparatus which applies a direct compressive force to the flexible portion of a container and measures the reaction force resulting from the internal pressure within the container.
Except for the '184 patent, the foregoing equipment is intended for operation and cooperation with conventional containers having simple geometric configurations such as cylinders, cubes or rectangular solids. Pressure application to complexly configured containers poses special problems. One such container which poses leak detection challenges is a cylindrical container having a relatively small length to diameter ratio wherein the two ends are sealed along flat, linear seals oriented perpendicularly to one another. Several testing schemes have been proposed for this container which typically receives a single serving of a semi-liquid material such as yogurt, ice cream or similar foodstuff.
One proposed method involves gripping the container in the palm of the hand, squeezing and visually observing any leaks. Aside from the possible untidiness of this method, a significant difficulty is short-term and long-term repeatability. Clearly, one tester during a given production shift and even more obviously, various testers over various shifts, will find it difficult to consistently pressurize the container and provide consistent leak detection results. Secondly, the test is not adaptable to automation. Accordingly, if a large number of production samples must be tested, the method will tax a human tester.
Other methods which have been proposed contemplate placing the container in a vacuum chamber and subjecting the container to a partial vacuum to determine leaking and seal integrity. While technically a suitable test procedure, evacuation of the vacuum chamber and cleanup necessitated by containers that burst can be time consuming.
It has also been proposed to test container seals by injecting air into the container and observing leaks or bursting. This test procedure requires that a needle be inserted in the test container, a step which is in itself difficult and which may alter the outcome of the test by disturbing the container. Furthermore, the test requires the disposal of the sample even if it exhibits good seal integrity.
The foregoing review of task specific leakage detection equipment prompts the conclusion that improvements in the art of same are both possible and desirable.